(a) Field of the Invention
The invention relates to an optical projection device, an optical projection display member and a manufacturing method thereof. More particularly, the invention relates to an optical projection device having high contrast, an optical projection display member and a manufacturing method thereof.
(b) Description of the Related Art
Current displays are developed towards trends as being light in weight while having large sizes. Accompanied with these trends, since projection displays have advantages of having small thickness and large sizes, projection displays are gradually replacing conventional televisions to become one of the predominant monitor products. Among various types of projection displays, back-projection displays are considered the most significant.
Monitors of present back-projection displays have the following main functional requirements:                (1) capability of expanding visible range for enlarging viewing angles of the monitors; and        (2) protective function over monitors for preventing effects that environment dust and humidity have on internal components of the monitors;        (3) capability of controlling reflections of external stray lights for elevating contrast of the monitors.        
Existing techniques for manufacturing monitors are indeed competent as easily achieving the requirements (1) and (2). However, these existing monitors yet fail to perform satisfactory outcomes while both accomplishing the requirement (3) as well as maintaining relatively higher effective light transmissivity.
Conventional monitors of back-projection display type are generally made by the method as disclosed in U.S. Pat. No. 2,378,252. Referring to FIGS. 1 and 2, a monitor 100 according to this prior technique has a light-absorbing substance layer 106 formed between an optical panel 102 and an optical sphere 104. Using the light-absorbing substance layer 106, external stray lights are absorbed and thus preventing reflections of the stray lights. Also, using the optical sphere 104 and the optical panel 102 to expand an angle of a light beam, so as to broaden the viewing angle.
However, this prior technique has inherent restrictions as described below. A Light beam incident from the back at a right angle, as shown in FIG. 1, it can easily penetrate through the entire screen. In addition, the light beam incident at an included angle θ, as shown in FIG. 2, it is prone to be absorbed by the light-absorbing substance layer 106, thereby lowering transmissivity thereof. It is observed from FIGS. 1 and 2 that, as the larger the incident angle θ of the light beam gets, a thickness of the light-absorbing layer 106 is increased from L1 to L2. Hence, efficiency of the entire monitor 100 is significantly lowered, or even homogeneity of the monitor 100 is also affected. Referring to FIG. 3, considering available techniques, an angle θ of a light beam incident to an optical projection assembly 108 can vary as high as from 20 to 30 degrees. Therefore, the difficulty as described above shall not be neglected.